Current very low with NEMA 17

Using Arduino Motors, Mechanics, Power and CNC
1

Hello,

I am completely new to Arduino and electronics in general.

I have:

  • arduino uno r3
  • nema 17 longrunner 17HD48002-22B
  • driver A4988
  • external power supply 12V 2A

I was able to make the stepper motor works perfectly but there is one thing that I don't understand.

I took a multimeter and measured voltage and current on the motor circuit.

Voltage close to 12V
Current is only 50mA, how is that possible?

The datasheet of this nema 17 shows that rated current is 1.7A (this is the reason I bought a 2A power supply), so I was expecting the motor to draw more...

Can anyone explain what is going on?

Thanks

2

You must set the current limit on the A4988 driver appropriately for the motor. Since the A4988 can handle only 1 Ampere per winding without additional cooling, that is the maximum possible.

Pololu has a good video explaining this, but the setting formula they give is valid only for their drivers, or an exact clone. Most clones and imitations are not exact. See the A4988 data sheet for the full details.

3

To set the current limit you will need to know the value of the sense resistor on your A4988 driver board. There are different Rsense values for different manufacturer's boards.

4

This is very helpful, thank you.

This is the A4988 I bought: https://www.amazon.es/gp/product/B071P41ZBW

Any idea how I could get the datasheet? I tried a google search but I'm not sure the datasheet I found are for this exact model...

5

What you need to know is the value of the current sense resistor. Post a clear, focused, close up photo of your driver, and hopefully a forum member can spot the resistor. It is one of the larger rectangular blobs on the PCB.

The formula for the current setting is given in the A4988 data sheet, and depends on the resistor value.

6

A4988
A4988925×1172 103 KB

Let me know if the picture is not good enough.

7

R4 and R5 are the sense resistors. They are 0.1 Ohm which is the value on many "clone" Chinese A4988 driver boards.

8

The current sense resistors are R4 and R5, 0.1 Ohm.

9

Thanks, everything is now much more clear.

10

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